The development of a network autonomous integrity monitoring positioning system in Malaysia

Abstract

Global Positioning System (GPS) is a space-based positioning, navigation and time distribution system designed for world-wide positioning and navigation applications. Accuracy of the GPS solution can be improved through Differential GPS (DGPS) technique that reduces errors in the GPS satellite signal. These errors are determined by Continuously Operating Reference Station (CORS) at precisely known station coordinates which will be transmitted in real-time as corrections to the user thus improving their position accuracy. To maintain the CORS system, the service provider needs to have a comprehensive quality and integrity monitoring mechanism in real time to ensure reliability of the system that would provide better service to users. The study provided a network based autonomous integrity monitoring (NAIM) system within the GPS National Research and Development CORS Network (NRCnet) area. A prototype of NAIM system in a web-based platform was developed to provide integrity monitoring for all CORS including information on CORS status, system level monitoring, user level monitoring and ground level monitoring. The web can be accessed by user via internet to check real-time status and integrity information of each NRC-net station. Besides, the user can monitor the accuracy of the station in term of DGPS fix rover precision shown in standard deviation in northing, easting and up component, thus increasing the confidence of users utilizing CORS data in realtime application. Two radio beacon stations of Sistem Pelayaran Satelit (SISPELSAT), namely Bandar Hilir Melaka (JLML) and Kuantan Pahang (JLKU) owned by the Marine Department of Malaysia were integrated into the NAIM system. By utilizing this system, the GPS data from JLML station were recorded for data accuracy and validation analysis continuously for 7 days. It was found that the accuracy of the JLML station for the north component was less than 1-meter, whereas the east component was less than 2-meters, and the up component had less than 3-meters. The data analysis proved that the station was in a good condition as it provided 100 percent DGPS fix and 2-meter accuracy on average. Based on the analysis, several tests and assessments were conducted towards NAIM system to evaluate the performance of SISPELSAT DGPS radio beacon services at the offshore and coastal areas of Peninsular Malaysia. At the offshore area, SISPELSAT stations, Melaka and Kuala Besar Kelantan had good conditions of more than 96 percent less than 1-meter accuracy and 80 percent of DGPS fix. However, Station Bagan Datuk had only 84 percent less than1-meter accuracy with 27 percent of DGPS fix. At the coastal area, the accuracy of DGPS fix observation at 21 reference stations was less than 2-meters which are directly proportional to the distance of the SISPELSAT stations. The study concludes that the factor of distance-dependent is significant towards the accuracy of the DGPS and influences the radio signal strength and Signal to Noise Ratio of SISPELSAT stations. Overall, the NAIM system has been shown to be capable of providing integrity monitoring mechanism and can be an alternative system for SISPELSAT.